1. Field of the Invention
The present invention relates to a gauge for verifying the operation of an apparatus for inspecting leads of an electronic package, and more particularly to a gauge for verifying the calibration and inspection parameters of a lead inspection apparatus for ball grid arrays.
2. Description of Related Art
The electronics industry is continually decreasing the size of electronic devices while increasing the pin count of the devices in an effort to increase the density of electronic packaging. Surface mount technology provides the industry with the ability to continue this trend since surface mount leads can be located relatively close to each other, as compared to through-hole technology. Common surface mount devices include ball grid arrays (BGAs), quad flat packs (QFPs), flat packs, gull-wing devices and the like.
As the pin count increases and lead spacing decreases, controlling mechanical parameters of the component leads, such as lead coplanarity, lead pitch, missing leads, lead deformation and the like, is critical for ensuring proper electrical interconnections when the components are installed on a printed circuit board. Consequently, lead inspection systems are utilized throughout the industry, from component manufacturing to printed circuit board assembly, for inspecting the leads of electronic packages to ensure that they meet their dimensional requirements.
Conventional lead inspection systems include infrared systems, laser scanning systems, gray scale camera systems and the like. Lead inspection systems typically analyze one or more mechanical features of an electronic package using various algorithms that compare the results of detector readings to predetermined parameter limits to determine whether the component is an acceptable or an unacceptable device. The accuracy of inspection systems, however, may be affected by several factors, including system calibration and programmed inspection parameters, that can lead to improper component acceptances and/or rejections with the potential result that a defective component is installed on a board or a perfectly good component is discarded as defective.
Since system calibration may change or drift over a period of time, it is necessary that system calibration be periodically tested and adjusted to alleviate any potential problems due to an improperly calibrated system. Calibration methods used in the industry, which typically utilize optics, 3-D triangulation sensors and lasers, require a considerable amount of time to calibrate a system. Consequently, an inspection system may not be calibrated often enough to ensure accurate electronic component inspections. Additionally, these calibration methods typically cannot be performed on-line and require a production line shutdown.
Even when an inspection system is properly calibrated, electronic components may still be improperly rejected or accepted due to an inspection process error. For example, an operator typically programs an inspection system with one or more predetermined inspection parameters to define the allowable limits against which a particular electronic package is compared when evaluating whether to accept or reject the component. When a parameter limit is incorrectly programmed into the system, a component can be improperly accepted or rejected even though the system calibration is accurate. Such process errors generally will not be discovered by testing the calibration of the system.
A xe2x80x9cgoldenxe2x80x9d component, which is an actual electronic component with known dimensions, may be used to verify the calibration and inspection parameters of an inspection system. However, the dimensions of the golden component leads can become altered due to handling and its repeated use as a verification unit. Verification units have been developed that are more robust than a golden component so that the unit may be more likely to maintain its mechanical parameters even with repeated use and handling.
U.S. Pat. Nos. 5,489,832 and 5,477,138 to Erjavic et al. disclose verification units which resemble certain aspects of quad flat pack and plastic leaded chip carrier type packages and are used for testing the calibration of a lead inspection system for such electronic packages. These units, however, are not suitable for verifying the calibration or process parameters of a lead inspection system for a ball grid array (BGA), including plastic and ceramic BGAs, micro BGAs and similar chip on board components.
In view of the foregoing, it is an object of the present invention to provide an improved device and a method for verifying the calibration and process parameters of a lead inspection apparatus for inspecting predetermined mechanical parameters of a ball grid array and similar chip on board components, and a method of manufacturing the device.
In one embodiment of the invention, a verification gauge is provided for verifying the operation of a lead inspection apparatus for inspecting leads of an electronic package that is comprised of a package body and a plurality of conductive leads arranged on the package body in a lead pattern. The electronic package has a predefined limit for at least one mechanical parameter of its conductive leads. The gauge has a predetermined mechanical relationship to the mechanical parameter of the conductive leads so that when the inspection system is used to inspect the gauge, the inspection system will provide a reading that is indicative as to whether the inspection system is properly set up for the at least one mechanical parameter.
In one illustrative embodiment of the invention, the verification gauge includes a gauge body having a plurality of apertures disposed on an outer surface thereof and a plurality of gauge lead members disposed in the plurality of apertures. The apertures are arranged to correspond to at least a portion of the lead pattern of the electronic package and at least a portion of each gauge lead member protrudes from a corresponding aperture by a predetermined amount beyond the outer surface of the gauge body. At least one of the gauge lead members has a predetermined mechanical relationship to at least one mechanical parameter of an electronic package.
In another illustrative embodiment of the invention, the verification gauge comprises a gauge body that is devoid of electronic circuitry, and a plurality of gauge balls arranged on the gauge body to correspond to at least a portion of the lead pattern, at least one of the gauge balls having a predetermined mechanical relationship to at least one mechanical parameter of a ball grid array.
In a further illustrative embodiment of the invention, a method of manufacturing the verification gauge comprises steps of providing a gauge base plate having a plurality of gauge holes extending therethrough that are arranged to correspond to at least a portion of the lead pattern of a ball grid array; providing a plurality of gauge balls; and placing the plurality of gauge balls in the plurality of gauge holes with at least a portion of each ball protruding from an outer surface of the gauge base plate. At least one of the gauge balls has a predetermined mechanical relationship to at least one mechanical parameter of the ball grid array.
In another illustrative embodiment of the invention, a method for verifying the operation of an inspection system for a ball grid array comprises steps of providing at least one verification gauge; inspecting the gauge with the inspection system for the at least one mechanical parameter; and determining whether the inspection system is properly set up for detecting when the predefined limit for at least one mechanical parameter is exceeded by a ball grid array. The verification gauge is comprised of a gauge body that is devoid of electronic circuitry, and a plurality of gauge balls arranged on the gauge body to correspond to at least a portion of the lead pattern, at least one of the gauge balls having a predetermined mechanical relationship to the at least one mechanical parameter of the ball grid array.
The gauge may be configured to substantially emulate the structural configuration, including the particular size, shape and lead pattern, of the electronic package. The gauge may be used to verify the calibration or the predefined limit of the inspection system for the mechanical parameter, including lead coplanarity, lead pitch, missing lead and lead deformation parameters. The gauge may be configured to be either xe2x80x9cacceptablexe2x80x9d, such that the gauge is within the predefined limit for the mechanical parameter, or xe2x80x9cnonacceptablexe2x80x9d, such that the gauge exceeds the predefined limit for the mechanical parameter.